Stool base



FIG. 1 is a front and right perspective view of a stool showing my new design.

FIG. 2 is a right side elevation view thereof; and,

FIG. 3 is a front elevation thereof, with the rear elevation being a mirror image of the front.

The broken lines in the drawings depict portions of the stool that form no part of the claimed design. 

CLAIM What is claimed is the ornamental design for a stool base, as shown and described. 